A catalytic converter for a vehicle comprises in general a canned and coated catalytic converter substrate in flow communication with inlet and outlet passages. It is positioned on the exhaust side of the internal combustion engine of the vehicle in order to treat exhaust gas emissions from the engine.
During cold start and warming-up of the engine, the catalytic converter is not sufficiently heated for optimum performance and the exhaust gas emissions may therefore pass through the catalytic converter without catalytic conversion thereof. To improve the heating properties, the catalytic converter is often positioned as close as possible to the exhaust ports. To accelerate heating, it is also possible to heat the catalytic converter electrically or to temporarily control combustion such that the temperature of the exhaust gas emissions is increased.
A frequent problem also particularly during cold start is that emissions in liquid form in the exhaust gas emissions do not participate in the engine combustion process. Gaseous emissions which condense on cold exhaust system surfaces present a similar problem.
Another problem in catalytic converters is that mixing of the exhaust gas emissions may not be sufficient, which results in an inhomogeneous mixture of the exhaust gas emissions passing the exhaust gas emissions sensors and reaching the inlet end of the catalytic converter. Optimum performance of the catalytic converter is negatively affected by an inhomogeneous mixture of the exhaust gas emissions. Furthermore, the exhaust gas emissions sensors will not provide the engine management system with correct feedback values.
A solution to one or more of the abovementioned problems used by some manufacturers is a so called hydrocarbon trap. Due to the fact that the catalytic converter substrate is not warm enough for catalytic conversion and that the concentration of hydrocarbon is high during cold start, a hydrocarbon trap where a trap material is coated on a typical catalytic converter substrate may be needed. The trap material stores hydrocarbon at low temperatures and releases hydrocarbon at higher temperatures. The trap material is, however, sensitive to ageing.
Another solution to the gas mixing problem may be to add a mixer or to compensate with complex software.
Finally, from US 2006/0008397 A1 it is known a space-saving exhaust gas aftertreatment unit allowing catalytic conversion for a relative long period of time even when there is only a small amount of installation space available.
In US 2008/0041036 A1, this prior art exhaust-gas aftertreatment unit is provided with an adding unit for adding, in countercurrent, a reactant flow to the exhaust gas stream to improve evaporation thereof.